Overheating your Mac Mini - No problem!

Bugbyte · 11-11-2006, 01:05 AM

If you've been curious about what happens when you overheat your Mac Mini, don't worry. I've done your homework for you!

I was on a lengthy trip this week with the Mini. My installation is particularly tight, buried in the dash, in close proximity with the heater/AC plumbing. You can check out my worklog by clicking my signature if you want all the gory details. Suffice it to say that because of the way my Mini is installed, it's actually more likely to overheat in the winter than the summer because it can suck in hot air from the heater.

So I've always monitored this by using temp monitor lite and making sure that I keep the heater set more to the feet than the upper vents (generally a 75% feet/25% upper split). Well, I forgot to do that this time and since this is the first time I've had the heat on in the car for an extended period of time, I overheated the Mini. Here's what happens.

It took about 35 minutes and the only warning I had was a single skip in the music about 5 minutes before overheat. I thought this was odd because I've NEVER had a skip in my audio, no matter what the conditions or load on the CPU.

Five minutes later the screen went black and the Mini shut down like somebody pulled the power cord. I instantly realized I'd had the vents set to all upper and had the temperature on full.

The mini docks in my dash and is removed via a lunchpail style handle I added to it. The handle is aluminum and when I reached into the dash to pull the Mini out it was almost too hot to touch! I pulled the Mini out and felt the top, bottom, sides. It felt like I'd baked it in the oven at 190 degrees.

I set it on the seat for 15 minutes until it cooled down and re-docked it, then hit the valet switch to energize the system. After a few seconds of silence, BONG! it started without complaint. I relaunched all apps and was back online with the SMART temp reading 118 degrees. Since I've routinely run it as high as 135+ F, I just monitored it for awhile and it stablilized at around 124F. I finished the trip (another 4-1/2 hours) and returned the next day with a 6 hour run. No problems with the system at all. In fact, I'm typing this entry on the Mini right now.

Thanks to whichever engineer decided that a thermal shutdown sensor was a good idea! It worked for me. Now, I suggest you don't test it yourself!

BarryWoods · 11-11-2006, 01:43 AM

That's good to know, might be time to add some insulation.

2k1Toaster · 11-11-2006, 01:57 AM

That's a resiliant computer! When I first read the thread title, I was thinking some pictures with flames shooting out your vents would be below! I am glad I was wrong!

Do you have any plans on fixing the circulation back there so that you can run your heater full blast and be ok?

Bugbyte · 11-11-2006, 11:51 AM

Quote: Originally Posted by 2k1Toaster

Do you have any plans on fixing the circulation back there so that you can run your heater full blast and be ok?

The problem is actually that the dash piece that connects the passenger vents to the heating system leak hot air into the dash, which is where the Mini picks up its intake air.

It's difficult to fix because the pieces don't mate until the dash is back on and there's very little room to get your hands around them to tape them up or whatever. Not only that, but you can't fix the leaks completely because the mechanism that makes the vent open or close operates using a slit in duct that leaks when it is in the open position but not in the closed position.

Anyhow, I can still run the heat full blast. I just have about 3/4 of it coming out the feet or I close the two center vents and it comes out the driver/passenger side. With seat heaters, I've never had an issue with being cold in the car because of that.

What I OUGHT to do is put temperature sensors in there and have the Mini monitor the intake temps and automatically adjust the air flow when it begins to warm up.

psedog · 11-12-2006, 04:35 PM

You really should look into insulating your vent system. It can help with the air leaks, just add a little bit of extra insulation where the two pieces will come together. It'll probably make it harder to put together, but the end result would be worth it.

godraj · 11-22-2006, 11:34 PM

bugbyte, do you have the ppc version or the intel version?

Bugbyte · 11-26-2006, 06:08 PM

Mine is PPC. Just got back from another long trip and paid very close attention to the temps as I was driving. It works quite well when you have it split between upper and lower vents. It actually runs a bit hotter when it is more biased toward the floor vents.

The temp I'm running consistently are in the 126-135F range. It seems to be happy at that range.

erikocc · 11-26-2006, 06:34 PM

just picked up a good piece of knowledge, and thanks to you, i didnt have to test it for myself! thanks for the pass-on..

godraj · 11-26-2006, 11:39 PM

bugbyte, i think if you had a intel, it would have fried the unit, or shut of alot quicker, becaue they run MUCH hotter. what are you using to read the temperatures?

GoHybrid · 11-27-2006, 12:17 AM

i can answer to the intel bit... they perform in exactly the same way in an overheat condition. My first round of testing had an intel mac positioned on it's side in my center console which is enclosed with little ventilation and that's exactly what happened. Thermally triggered shutdown followed by a brief cooldown, then flawless operation. Still works to this day, however I've since relocated it to the glove compartment which has more air movement and sees temps closer to that of the cabin.

Bugbyte · 11-27-2006, 11:46 AM

Quote: Originally Posted by godraj

bugbyte, i think if you had a intel, it would have fried the unit, or shut of alot quicker, becaue they run MUCH hotter. what are you using to read the temperatures?

I'm using an app called Temperature Monitor Lite. The PPC box (and I think the Intel one, too) doesn't have a direct processor temperature. Instead, the app reads the temperature of the S.M.A.R.T. sensor inside the disk drive. Therefore, all of my temps are of the drive temp, NOT the processor temp.

All I really know about it is that it seems to run okay when the drive temp is below 140F but I have no idea whether the processor is hotter or cooler than that.

DrZiplok · 11-29-2006, 12:01 AM

The intel Mini is quite capable of looking after itself; in normal operation it won't allow itself to overheat (due to internal heat sources - can't speak for leaving it on your parcel shelf). If it does get too hot to be happy, as you've noted it will turn itself off long before any permanent damage is done. The CPU itself has specific protections related to overheating above and beyond those in the SMC.

In normal operation it runs hot because that makes it quiet. The target temperature leaves plenty of margin on the components - Apple is pretty careful about specifying that sort of thing. It's certainly an alien concept to many folks coming from the PC world where the approach is "keep everything as cold as possible" - instead, the device is engineered with full knowledge of how the components age vs. heat and time.

kandyman676 · 12-04-2006, 01:57 AM

Quote: Originally Posted by Bugbyte

I'm using an app called Temperature Monitor Lite. The PPC box (and I think the Intel one, too) doesn't have a direct processor temperature. Instead, the app reads the temperature of the S.M.A.R.T. sensor inside the disk drive. Therefore, all of my temps are of the drive temp, NOT the processor temp.

Actually, the Intel chips can have their temps read on the CPU. Each system build has more or less sensor then the other, and they are "undocumented" to boot. The OS obvious knows about them. Most of the 3rd party temp monitors have updates now that include the patch to get around the "blocking" of the temp monitors. each new minor release (i.e. 10.4.7 to 10.4.8) sometimes alters their access.

From having a MacBook Pro that had bad thermal paste applied and a bad fan controller (which all was repaired by AppleCare), I can attest that their thermal sensor for shutdown works as directed in protecting the hardware. I was getting temps of around 155+ F before it would shut down.

DrZiplok · 12-07-2006, 03:13 AM

Quote: Originally Posted by kandyman676

Actually, the Intel chips can have their temps read on the CPU. Each system build has more or less sensor then the other, and they are "undocumented" to boot. The OS obvious knows about them.

The on-die temperature sensor is mostly useless for thermal management; it is non-linear, has poor resolution, and it's not calibrated. It exists to support the processor's internal thermal protection mechanism, but apart from a couple of 'calibrated' trip points you can't draw any reliable conclusions from the numbers it gives you.

Thermal management in Apple's systems is handled by the SMC, which co-ordinates a varying number of sensors depending on the system. The Mac Mini's thermal management is fairly primitive compared with the portables (the MacBook Pro systems have more than ten thermal sensors scattered around the chassis).

From the Mini's perspective, the most important sensors are the one on the CPU heatsink and (if I remember correctly) one on the board over by the DIMMs. The default thermal policy is to keep these components well inside their thermal limits but also keep the fan as slow as possible.

Quote:

Most of the 3rd party temp monitors have updates now that include the patch to get around the "blocking" of the temp monitors. each new minor release (i.e. 10.4.7 to 10.4.8) sometimes alters their access.

It's not so much a matter of blocking as that there is no exposed interface for this information. Happily, that hasn't stopped folks from realising that the Apple components communicate this information between one another, and there's nothing that makes a third-party developer any less smart. 8)

= Mike

kandyman676 · 12-08-2006, 10:46 PM

Yes, what you said:-) LOL. I just had barely scratched the surface when my MacBook pro was having heat problems and ran into some of the things you said, but they never told EXACTLY as you did. :-)

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